This is an application from a leading investigator in Borna disease virus (BDV) biology representing a competing renewal of a highly productive grant that represents the PI's major source of funding for basic research in BDV molecular biology and pathogenesis. The broad objective of the effort is to characterize BDV and to define viral and host factors that contribute to: (1) the low productivity of BDV infection, (2) its capacity to generate persistent infection, and (3) BDV neurotropism. The five specific aims include: (1) functional characterization of the BDV P protein, (2) analysis of BDV protein- protein interactions, (3) characterization of the BDV X protein, (4) isolation and characterization of cellular element (PRCE) binding proteins, and (5) establishment of a reverse genetic/recombinant BDV system.